1. Field of the Invention
The present invention relates to an apparatus and method for detecting scene changes using the difference of mean absolute difference(dMAD) between image frames.
2. Description of the Prior Art
In general, scene change data is very useful for predictive coding of digital image signal, and intraframe coding should be performed for the first frame after a scene change since the occurrence of the scene change makes prediction of current frame over previous frame invalid.
Scene change data in Macro Block unit is utilized most usefully for bit rate control process of image encoder, which applies intraframe encoding mode or interframe predictive coding according to their characteristics. If there is no scene change detection process, most macro blocks of the first frame after the scene change will actually be processed under intraframe coding mode even if it is originally under interframe predictive coding mode. In this case, the balance of bit rate control will be broken due to the generation of data which far outnumbers the number of bits targeted. Additionally, the quality of the image after the current frame will be downgraded considerably. So, for adaptation predictive coding, it is very important to choose either intraframe coding or interframe coding by doing scene change judgement before coding each frame. As criteria for scene change, difference of frames, correlation between frames, average brightness of frame, quantitization control characteristic curve, and so on, are generally used because of easiness of evaluation.
FIG. 1 shows flow chart of conventional cases for scene change judgement using interframe difference.
As shown FIG. 1, the scene change judgement method includes step 1 for calculating the value of MAD between previous frame and current frame, step 2 for comparing the resultant output generated in the step 1 with threshold value, step 3 for estimating to be occurred scene change when the resultant output generated in the step 1 is greater than the threshold value, step 4 for estimating to be not occurred scene change when the resultant output generated in step 1 is smaller than or equal to the threshold value. Scene change data given from the steps 3, 4 could be utilized for bit rate control of encoder. In the conventional method, there is a high possibility of misjudgement for the scenes moving in the wide range that scene changes for almost every frame have occurred even though no scene changes have actually occurred. This is because it is difficult to distinguish them from virtual scene change due to MAD of each frame greater than threshold value when the scenes are moving in the wide range.